Conventionally, technologies for supplying a cryogenic liquid such as liquid nitrogen to a container that contains a superconducting coil or the like in order to maintain the superconducting coil in a cryogenic state have been known. In these technologies, a relief valve is provided for releasing the fluid out of the system so as to prevent damage to the system that may be caused by an excessive fluid pressure in a flow passage (see Patent Literature 1). In addition, because a maximized load or fluctuating load of pulsative pressure may possibly cause failures due to insufficient pressure resistance or fatigue, conventionally, adamper is provided in the piping system that supplies a cryogenic liquid in order to suppress the pressure fluctuation (see Patent Literature 2).
However, in the conventional examples mentioned above, due to a heat exchange that occurs in the parts such as the relief valve or damper and an unwanted release of the cryogenic liquid by the relief valve, decrease in cooling efficiency or reduction of liquid amount may be caused. There is yet another problem in which the relief valve does not function properly due to the icing of moisture or the like in the atmosphere.